The present invention generally relates to a composite material for a microwave heating container and, more specifically, to a microwave heating container which minimizes both the amount of microwave energy reflected and the amount of microwave energy absorbed by the container.
Microwave energy can be reflected, absorbed, or passed through the walls of a cooking container. The relative degree of which each is desired depends on the application. Coatings or materials that primarily reflect microwaves are used as a shielding for electrical components and antenna. Shielding materials are not good for cooking containers because the energy is not transmitted to the food within.
Coatings or materials that primarily absorb microwave energy become heated. These heated surfaces are useful for browning the surface of relatively low moisture, solid foods. Absorbing surfaces are not useful for heating high moisture foods such as soups, sauces, or batters. The amount of energy absorbed can be measured by the "loss tangent". Materials having a loss tangent of less than 10.times.10.sup.-4 do not absorb appreciable amounts of energy and do not become hot during use.
Microwave reflection can be explained by looking at the rate of change of the dielectric constants between different transmission media. Ideally, one would design a container having a smooth gradient of dielectric constants between air (k=1) and the contained food. Such a container would be expensive and impractical.
It would be desirable to have a material and microwave cooking container made therefrom which would transmit microwave energy without substantial reflection or absorption.